1. Field of the Invention
The present invention relates to a semiconductor light emitting device using a light emitting element such as a light emitting diode (LED).
2. Description of the Background Art
A semiconductor light emitting device of this kind is disclosed for example in Japanese Patent Laying-Open No. 2000-269551.
This conventional device typically has a structure of a surface mounted LED as shown in FIG. 12. In this conventional structure, a resin b to fix a lead frame a is formed by insert molding or the like. On lead frame a, an LED chip c is electrically and mechanically connected by means of an Ag paste f and a gold wire d. The circumference of LED chip c is protected and sealed with an epoxy resin e.
In this conventional semiconductor light emitting device, lead frame a is formed to have a designated pattern shape, plated with Ag, and then insert molded into resin b. On lead frame a, LED chip c is electrically and mechanically connected by means of Ag paste f and gold wire d. Then, LED chip c is sealed with epoxy resin e or a silicon resin. After an unnecessary lead portion is cut, lead frame a is bent into a U shape, and thus a terminal portion for joining with a mounting board is formed.
Examples of such a semiconductor light emitting device include a device having one or a plurality of LEDs emitting light in a single color such as red, blue, or yellow, or emitting white light generated by exciting a blue LED with a fluorescent substance (for example, a device having two red LEDs); and a device of RGB (red, green, and blue) light emitting type in which three LEDs emitting light in each of three primary colors (a red LED, a green LED, and a blue LED) are mounted into one product (for example, see Japanese Patent Laying-Open No. 08-153895).
Of the conventional devices as shown in FIG. 12, the device having a plurality of LEDs of white light emitting type each formed by exciting a fluorescent substance with blue LEDs, and the device of so-called RGB light emitting type having three LEDs emitting light in each of three primary colors (a red LED, a green LED, and a blue LED) are often mounted mainly in a light source for a supplementary light of a CCD (charge-coupled device), or in a light source for backlighting liquid crystal. Since each of these conventional devices has advantages and disadvantages as described below, it has been difficult to produce an LED having high brightness and excellent color rendering properties.
(1) The device having LEDs of white light emitting type each formed by exciting a fluorescent substance with blue LEDs:
The device of this type features good light emission and conversion efficiency, and it can obtain high brightness easier than the device of RGB light emitting type which generates white light by combining the three primary colors (red, green, and blue). At the same time, since the device of this type generates white light in a pseudo manner in combination with a yellowish green component generated by exciting a fluorescent substance with blue LEDs, it contains almost no red component. As a result, the device having LEDs of white light emitting type has poor color rendering properties, and in particular it cannot provide bright red color.
Although some fluorescent substances allow the device of this type to have a red component, using such a fluorescent substance to achieve the above effect involves poor efficiency. Accordingly, further improvement is required for practical use. Furthermore, since the device having LEDs of white light emitting type cannot display individual colors such as blue, green, and the like, its application is limited.
(2) The device of RGB light emitting type having LEDs emitting light in each of the three primary colors (a red LED, a green LED, and a blue LED):
Since the device of this type contains three primary color components, it has excellent color rendering properties. Thereby, it can in particular provide bright red color when used for shooting with a CCD, backlighting liquid crystal, or the like. Further, since the device of this type has a red LED, a green LED, and a blue LED individually, color balance can be adjusted. As a result, the device of this type can reproduce individual colors and generate various colors, and thus it is also excellent as an illumination. However, when compared with the device having LEDs of white light emitting type each formed by exciting a blue LED with a fluorescent substance, it is difficult for the device of this type to achieve brightness due to a problem in individual light emission efficiency.